Various gene expression promoters such as CMV and CAG promoters have been developed to increase gene expression efficiency (Patent Documents 1-4). However, in the field of biotechnology, even when these conventional techniques are used, problems regularly occur, such that almost no gene expression takes place or the amount of the thus expressed protein is extremely low, depending on cell types or gene types. These problems cause big barriers to the development of medical care using gene expression for diagnosis or treatment.
Meanwhile, the REIC/Dkk-3 gene is known to be a gene relating to cell immortalization. It has been reported that the expression of this gene is suppressed in cancer cells. It has also been reported that the REIC/Dkk-3 gene has been used for cancer therapy (Patent Document 5).